Investigation On Feeding Ecology And Habitat Characteristics Of Bigeye Tuna (Thunnus Obesus) In The Eastern Pacific Ocean

Bigeye tuna (Thunnus obesus) is one of the main target species in the pelagic tuna fishery inthe Pacific Ocean. The Pacific tuna fishery is managed by Western and Central Pacific FisheriesCommission (WCPFC) and Inter-American Tropical Tuna Commission (IATTC). The bigye tunastock in the eastern Pacific Ocean has been fully exploited and close to over-fishing. Improvementof understandings of bigeye tuna biology and habitat is very important to help stock assessmentand management of this stock.In this study, using bigeye tuna samples (n=2585) collected in the South-East Pacific longlinefishery (16°S-32°S,108°W-125°W) during September2010-March2011and September2013-January2014. I studied the feeding ecology of bigeye tuna including feeding time, feedingstatus by size, stomach contents composition, feeding quantity, digestive status. I used the TDR totest the hook depth and temperature of sea water and get the environment of bigeye tuna, and thenfind the best hook configuration. Using fishery data from bigeye tuna fishery in the South Pacific,combined with satellite remote sensing of sea surface temperature, and the data of temperature andsality of sea water from10to300m below the sea, the relationship between fishing ground andocean environment was analyzed. The key results are as follow:(1) The prey species of bigeye tuna included fish, cephalopods, crustacean and other species. Theprimary prey component of the diet was fish (accounting for48%), cephalopods (24%), andcrustacean (13.33%). The dominant species of food contents were Sternopiyx diaphana,Gemplus serpens, Ranzania laevis, and Chanos chanos.(2) From the horizontal direction：The analysis of the relation-ship between monthly catchstatistics and average SST indicated that the favorite monthly SST of the bigeye tuna longlinefishing-grounds is25～27℃.(3) From the vertical direction：Study the temperature, depth and salinity relationship withfeeding activity. The result were as follow: depth217～303m, temperature15.5～18.7℃,salinity34.81-35.31. The main thermocline of this area was deeper than200m from2014September to December. The layer of thermocline became more complicated from September to December. The most shallow layer was in December, the first layer appeared in the depth230m, the deepest thermocline layer was340m. The characteristic of thermocline was moredense and shallow in September and December, Deeper and wider in October and November.